Median preoptic nucleus and subfornical organ drive renal sympathetic nerve activity via a glutamatergicmechanism within the paraventricular nucleus.

Am J Physiol Regul Integr Comp Physiol. 2012 Feb 15;302(4):R424-32. Llewellyn T, Zheng H, Liu X, Xu B, Patel KP. “The paraventricular nucleus (PVN) of the hypothalamus is involved in the neural control of sympathetic drive, but the precise mechanism(s) that influences the PVN is not known”. The authors hypothesized that glutamatergic activation of higher brain centers such as the median preoptic nucleus (MnPO) and subfornical organ (SFO) could influence PVN. To test this hypothesis, the authors performed several microinjection experiments. First they injected a retrograde tracer into the PVN and visualized it in the MnPO and SFO confirming a neuroanatomical connection. Second they activated MnPO by microinjection of NMDA or bicuculline and demonstrated an increase in RSNA, blood pressure and heart rate. To test whether these effects are mediated through PVN, they blocked PVN using AP5 (glutamate receptor blocker) and repeated the experiment and found MnPO activation after blocking PVN does not produce the same cardiovascular effects, suggesting the effects are mediated through PVN. Further firing activity of PVN neurons were tested by activation of neurons in the MnPO. Finally, similar to MnPO, SFO was activated before and after blockade of PVN. Changes in RSNA, blood pressure and heart rate were recorded. The findings from this study suggest that glutamatergic activation of the PVN is at least partially mediated by activation of MnPO and SFO. -Madhan